Panels used in automobiles or the like are required to be light-weight. To provide a light-weight panel, the plate thickness may be reduced, for example. However, reduced plate thickness leads to decreased rigidity. In view of this, proposals haven been made to provide recesses and protrusions to provide a certain rigidity without increasing plate thickness. The recesses and protrusions are required to be shaped so as to improve rigidity with the minimum depth in order to avoid contact with other components.
Japanese Patent No. 5218633 discloses a panel. The panel includes a plurality of protrusions and a plurality of recesses. Each protrusion has a flat top surface. Each recess has a flat bottom surface. The protrusions and recesses are in rows and columns, where the protrusions and recesses in each row are arranged alternately and the protrusions and recesses in each column are also arranged alternately.
JP 2012-51004 A discloses a plate having recesses and protrusions. This plate includes a plurality of protrusions and a plurality of recesses. Each protrusion has a flat top surface. Each recess has a flat bottom surface. Each of the top and bottom surfaces has a pair of extending portions and a connecting portion connecting the extending portions. The protrusions and recesses are in rows and columns, where the protrusions and recesses in each row are arranged alternately and the protrusions and recesses in each column are also arranged alternately. In plan view, each of the extending portions of one of a top surface and a bottom surface is located between the extending portions of the other.
Japanese Patent No. 4402745 discloses a heat insulator. The heat insulator includes a large number of, protrusions. Each protrusion is hexagonal in shape in plan view, and the vertical cross section that passes through opposite vertices is arc-shaped. The portions of the flat plate located between the protrusions are not shaped as a straight line.
JP 2011-27248 A discloses a plate having recesses and protrusions. In this plate, each recess/protrusion includes a first region, a second region and a third region with different protrusion heights as measured in the thickness direction. These regions are distributed such that regions of the same type are not arranged in a continuous manner and each region is contact with two other regions of a different type.
JP 2011-101893 A discloses a plate having recesses and protrusions. In this plate, each recess/protrusion has a first protruding portion, a second protruding portion and an intermediate face. The first protruding portion is shaped as a dodecagonal pyramid or a truncated dodecagonal pyramid. The second protruding portion protrudes in a direction opposite to that of the first protruding portion and is shaped as a hexagonal pyramid or a truncated hexagonal pyramid. The intermediate face is a rectangular face provided in the intermediate reference plane.
JP 2011-110847 A discloses a plate having recesses and protrusions. This plate includes first columns each having first regions and intermediate regions arranged alternately to form a straight line, and second regions and intermediate regions. Such first and second columns are arranged alternately. The first regions in a first column are adjacent to the intermediate regions in a second column. The second regions in a second column are adjacent to the intermediate regions in a first column. The first and second regions are connected by first skirts. The intermediate regions and first regions are connected by second skirts. The intermediate regions and second regions are connected by third skirts.
JP 2011-110954 A discloses a vehicle panel. The vehicle panel includes an interior panel. The interior panel includes recesses and protrusions. Each recess/protrusion has a first protruding portion, a second protruding portion and an intermediate face. The first protruding portion is shaped as a dodecagonal pyramid or a truncated dodecagonal pyramid. The second protruding portion protrudes in a direction opposite to that of the first protruding portion and is shaped as a hexagonal pyramid or a truncated hexagonal pyramid. The intermediate face is a rectangular face provided in the intermediate reference plane.